The present invention relates to a throttle control for a carburetor or the like fuel/air mixing apparatus, intended particularly for a power saw and provided with a throttle valve device and a choke valve, in which the choke valve is adjustable between a normal idling position and a cold starting position.
In several carburetor applications it is necessary that the throttle valve is arranged automatically to return to its idle position. In several of these cases, for example where the motor is started by hand, it is necessary that the throttle valve device is provided with a retaining member, which makes it possible to retain the valve in a position appropriate for starting. In order not to take away the effect of an automatically returning throttle control it is necessary also that the retaining member is arranged to return automatically. This has usually been arranged in that the motor has been provided with a particular control adjacent the throttle by means of which the retaining member is operated. The handles of power saws with control means have in recent years often been made vibration-free relative to the motor and the implement driven thereby. The throttle control has become movably suspended in relation to the motor which has raised difficulties in obtaining a well defined starting position for the throttle control. On the market there are examples of machines where different specimens of the same model have different motor speeds in the magnitude of 100 rps with no motor load and with the throttle control arrested in starting position. This condition is highly unsatisfactory on one hand as the motor will race to speeds which can be detrimental, particularly to a cold motor and on the other hand as the high speed can cause accidents. A choke device must usually be used when cold starting a motor. Motors equipped with throttles as mentioned above thus have three different controls, which must be operated, i.e. a throttle control, a retaining member and a cold choke control. The choke control must be returned manually as soon as the motor ignites and it is often necessary thereupon to restart the motor.
The choke must in order to avoid motor failure be arranged in such a manner that during running it cannot return to the cold starting position e.g. upon influence from vibrations caused by the motor. Motors are oftenly provided with means adapted to prevent such return.